THE best way to experience all that is strange and a little otherworldly about downtown Detroit is to walk the streets around 5 p.m. on a weekday. At that hour, you’ll notice not just the peculiarity of what is around you — notably, the gorgeous, Art Deco skyscrapers alongside empty, decrepit buildings — but also what is missing. There is no traffic here. As the workday ends, cars trickle out of underground parking lots and speed off to nearby highways, but in a volume that doesn’t cause delays.